The improvement to be described in this application was originally devised for the purpose of accurate metering of seed (and/or fertiliser) within an agricultural seeding or sowing machine (herein called a “Seed Drill” or “air seeder”) that creates rows of planted seeds over a field. In many countries, cultivation of food plants is practiced on a large scale. For example, Australia grows about 26 million tonnes of wheat each year; the actual amount being somewhat dependent on conditions. China grows about 10 times as much, though under more intensive management. The inventor has developed some improvements to machinery intended to be towed behind a sufficiently powerful tractor across a field, while providing controlled seed spacing, row spacing, fertiliser depth, seed depth, and fertiliser amount.
An air seeder includes storage means or hoppers for seeds and usually also for concurrently applied fertiliser. Typically it has number of units called openers, each including a fertiliser tine to cut into the soil and discharge granular material beneath the soil surface. A following seed tine is used to cut into the soil and discharge seeds. Refer to the web site www.ausplow.com.au/prod/_info/how and similar pages for an introduction to current technology (downloaded on 31 Aug. 2014). Another useful background document is “An Investigation of air seeder component characteristics” at http://wwwl.agric.gov.ab.ca/$department/deptdocs/nsf/all/eng8060, downloaded on 2 Sep. 2014. Problems may be exacerbated when the air seeder is scaled up, having perhaps 20 openers on each side of a drawbar, each provided with a seed tine. If rows are missed or under-filled the crop yield cannot reach an optimum, while if the seeds are placed too close together they compete for nutrients, water and light. Again, the crop yield cannot reach an optimum. Likewise, too little or too much fertiliser reduces optimums. Therefore, metering of inputs is an important aspect of a cropping operation.
Seed flow sensors to monitor the process near the point of deposition are known, and are retained in this invention. It is highly preferable to provide an air seeder that will run for long periods without interruption for optimised machine, seed and operator productivity. Problems arising in existing apparatus include irregular seed spacing along a row; often because a metering mechanism inside the machine becomes unreliable, perhaps being clogged by wet or hygroscopic materials, or litter, and fails to deliver seeds at a suitable rate into the associated seed tine. The same problems may also occur in relation to metered fertiliser.
The prior art includes some consideration of accurate metering of seed (and/or fertiliser) for an air seeder. This problem has been addressed in a number of ways, as reviewed in “An Investigation of Air Seeder Component Characteristics” (see above).
In Australia it is a common practice to rotate crops; advantages include improved weed and disease control. One preferred 4-season rotation scheme is three seasons of wheat, then one season of canola. Agricultural machinery that can be switched between sowing wheat and sowing canola would be useful. Yet the seed sizes are very different. Also, sowing rates are different. Wheat is typically applied at 100 kg/ha whereas canola is applied at 3 kg/ha. A further problem to be solved within this invention is to provide a sowing machine capable of being set up for sowing “normal seeds” such as wheat, and “fine seeds” such as canola as the occasion demands.